Field of the Invention
The invention relates a semiconductor device and a manufacturing method thereof, and particularly relates to a thin film transistor and a manufacturing method thereof.
Description of Related Art
Most display panels use an amorphous silicon (a-Si) thin film transistor or a low temperature polysilicon (LTPS) thin film transistor as a switching device of a pixel structure. However, an oxide semiconductor thin film transistor has high carrier mobility compared to the amorphous silicon thin film transistor, and the oxide semiconductor thin film transistor has better threshold voltage uniformity compared to the low temperature polysilicon thin film transistor. Thus, the oxide semiconductor thin film transistor has been applied to a high-quality display panel.
To reduce a number of masks required to manufacture the oxide semiconductor thin film transistor, some people use half tone mask technology to manufacture the oxide semiconductor thin film transistor. The current manufacturing method of the oxide semiconductor thin film transistor is as follows. First, a gate is formed on a substrate. Next, a gate insulating layer is formed on the substrate to cover the gate. Then, an oxide semiconductor layer is formed on the gate insulating layer. Then, an etching stop layer is formed on the oxide semiconductor layer. Then, a photoresist structure having a thin portion and a thick portion is formed on the etching stop layer using a half tone mask. Then, the etching stop layer and the oxide semiconductor layer are patterned using the photoresist structure as a mask to form a first etching stop pattern and an oxide semiconductor pattern. Then, an ashing process is performed to remove the thin portion of the photoresist structure and retain a portion of the thick portion to expose a portion of the first etching stop pattern. Thereafter, the first etching stop pattern is patterned using the remaining thick portion of the photoresist structure as a mask to form a second etching stop pattern. The second etching stop pattern exposes two sides of the oxide semiconductor pattern. Then, the remaining thick portion of the photoresist structure is removed to expose the second etching stop pattern. Thereafter, a source and a drain are formed on the second etching stop pattern to complete the oxide semiconductor thin film transistor. However, when the first etching stop pattern is patterned to form the second etching stop pattern, a portion of the gate insulating layer not covered by the oxide semiconductor pattern will be removed, which affects the yield of the thin film transistor.